1. Field of the Invention
The invention relates to methods for shifting a vehicle transmission.
2. Background Art
A powertrain system for a vehicle generally includes an engine and a multi-ratio transmission. An output shaft of the engine is mechanically coupled to an input shaft of the transmission. Before shifting from a first gear to a second gear, the input shaft may need to achieve a target speed. The target speed is based on the gear ratio associated with the second gear and the speed of an output shaft of the transmission. Fuel supplied to the engine is temporarily reduced or eliminated to reduce the input shaft speed to the target speed. The shifting process is completed when the input shaft speed approaches the target speed. The time for the input shaft speed to reach the target speed depends on the dynamics associated with the operation of the engine.
In one example, the process of shifting the transmission involves disengaging a dog clutch from a first gear and subsequently engaging the dog clutch with a second gear. Engaging the second gear may be accompanied by a lurching movement caused by slack in gearing of the transmission. Shifting with a dog clutch may cause large fluctuations in the speed of the output shaft of the transmission.